This invention relates to magnetic tape cassettes or cartridges, such as the type commonly used in video cassette recorders. The invention is particularly concerned with a reel spring, slack limiter and tape guide for a magnetic tape cassette.
Reel springs are used in a cassette to rotatably mount the tape reel shafts. Prior art reel springs are shown in U.S. Pat. Nos. 4,544,062 to Maehara, 4,593,868 to Sato et al. These springs have a generally rhombic outline, either with or without internal cutouts. One of the difficulties with such a spring configuration is the amount of waste associated with its manufacture. These springs are typically stamped out of a continuous strip of metal. With a rhombic spring outline a significant portion of the metal strip is trimmed away and discarded. Sato et al recognizes this problem and provides a spring configuration which reduces the amount of material lost. The present invention affords further material cost savings over the structure in Sato et al.
The magnetic tape cartridge will also typically include a slack limiter in the form of either a wiper tab or brake, for vhs or beta cassettes, respectively. The slack limiter preloads the magnetic tape so that it will not unwind inadvertently. The slack limiter must provide sufficient tension on the tape, but at the same time it must not generate too much friction which would cause high operating loads and excessive wear. In the past, slack limiters have been made of metal or polyester but these must be coated with polytetrafluoroethylene (ptfe) to obtain the desired frictional characteristics. This technique has two disadvantages. First, ptfe is relatively expensive and its attachment to the slack limiter adds extra steps in the manufacturing process. Second, the adhesive used to secure the ptfe to the wiper tab inevitably leaks out and contaminates the magnetic tape. An example of this construction is shown in Saito, U.S. Pat. No. 4,290,567. Saito also discloses a slack limiter having a free end portion which is bent back on itself and which is formed from a strip of suitably resilient plastic having carbon or graphite or other material which produces a low coefficient of friction at the free end. Thus, in this embodiment, Saito eliminates the ptfe bearing material.
The tape guides direct the tape's entry and exit from the cassette housing at the access opening. This involves wrapping the tape about the guides with resultant contact between the tape and guide at a substantial portion of the guide's periphery. To minimize tape wear it is desirable to have a highly polished finish on the guide surface in contact with the tape. In the past this has been accomplished by making the guide out of a polished stainless steel tube. However, fabricating such a tube or rolled stamping with its critical diameter and polished finish is a time consuming and expensive undertaking. Further, the full polished tube provides expensive material at areas of the guide which will never be in contact with the tape. Also, the mechanical strength required of the full tube necessitates use of a greater wall thickness than required strictly for the bearing function. The present invention alleviates these problems.